1. Field of the Invention
The present invention relates generally to switching apparatus, and, more particularly, to a thermocouple selection switch for monitoring thermocouples positioned within tunnel furnace cars.
2. Description of the Prior Art
In the processing of various metal products, heat treating furnaces are required to allow treatments such as annealing, hardening, tempering, carburizing, and stress relieving of the metal stock. For these treatments, the furnaces are operated at temperatures ranging from several hundred degrees Fahrenheit to temperatures close to two thousand degrees. Critical to the success of the heat treatment is the maintenance of a uniform temperature in the furnace to allow even heating of the metal stock.
One example of a heat treating furnace is a tunnel furnace. In such a furnace, the stock to be heated, such as metal coils, is placed inside a series of furnace cars which are pushed slowly in a sequential manner through the furnace. As the furnace fills with these cars, insertion of additional furnace cars into the furnace causes the first cars inserted into the furnace to be pushed out of the furnace.
To ensure that the stock is uniformly heated, the temperature within the individual furnace cars is periodically tested. Thermocouples are mounted within the furnace cars to allow this interior temperature to be determined. Thermocouples are typically positioned above or beneath the metal stock in the furnace cars, and periodic readings of these thermocouples allow temperature profiles of the metal stock to be compiled.
Sidewall fixtures positioned along the sidewalls of the tunnel furnace shell allow an external probe to be inserted therethrough to connect with the thermocouples in order to obtain readings from the thermocouples. The connection to the thermocouples is accomplished by a conventional plug-in connection with the external probe having a plug positioned at the end thereof and a mating socket mounted beneath the furnace car.
Such a means of connection with the thermocouples requires the individual furnace cars to be precisely aligned with the probe. Oftentimes, however, readings are attempted when the furnace car is misaligned with the probe. Such a misalignment at times precludes an electrical connection with the thermocouples, or, results in damage to the probe and/or the mating socket on the furnace car.
It is therefore the object of the present invention to provide a means for connecting an external probe to a thermocouple positioned within a tunnel furnace car while not requiring the car to be precisely positioned relative to the probe.
It is a further object of the present invention to provide a thermocouple selection switch to allow the monitoring of any of a plurality of thermocouples positioned within a tunnel car.